The present invention relates to a method of granulating water soluble fertilizers with high kieserite content.
For soils impoverished in magnesium it has been recommended to use the fertilizers with kieserite and other soluble fertilizers with high kieserite content, since the magnesium ion from the water soluble magnesium sulfate hydrate is easily available for the plant roots. The modern fertilizer technique involves bringing the fertilizers in a granulated form.
The granulation of kierserite and kierserite-rich mixtures by a rolling system has been recognized as very difficult. The cause of it is the physical-chemical properties of the kieserite. The German Patent No. 3,618,058 proposes a solution in accordance with which a granulating aid means from the class of the saccharide is added to the optimal grain existing kieserite-rich granulating material. This proposal can be used not only during the rolling granulation in granulating laboratory, but also in mass production with good results.
During granulation of mass fertilizers, the price of the granulating aid means plays a considerable role. Moreover, the constant availability must also be considered. This is not the case for many saccharide containing waste products, since they are produced in different seasons and have a limited storage ability.
Therefore, there is a task, in accordance with alternative aid means for favorable influence of the formation of granules by rolling, to find a moist kieserite-rich granulating mixture which insures the strength of the granules over a long time period.
A methodical alternative to the rolling granulation is a press granulation which however in the case of kieserite-rich fertilizers in the absence of alkali chlorides encounters special difficulties. This deals with the rigidity of the crystal lattice of the crystalline kieserite particles.
For overcoming the above-mentioned difficulties it was proposed in the German Pat. No. 3,148,404 to add to the kieserite a solution of potassium sulfate or of alkali silicates, borates or phosphates before the pressing. This features leads to an improvement of the shell formation and the quality of the kieserite granulate produced by breakage of the shells. The thus obtained progress is however not sufficient to insure a lasting use of the process in this technique.
It was then attempted to transfer the experience collected during pressing to rolling granulation, despite the fact that the process of the granulation is here totally different. With the use of soldium sulfate for moist granulating mixture, a sufficient granule formation can be achieved only with a properly high dosing of the sodium sulfate. The high quantity of use is disadvantageous since in connection with the high residual moisture which must be allowed for stabilization of the binding in the granules during drying, the material content of the granules becomes sensitive. The transmission of the experience obtained during the pressing granulation to the rolling granulation has been questioned during a long time.